Printed circuit board filter having rows of vias defining a quasi cavity that is below a cutoff frequency

摘要

A low frequency reject filter element is formed on a printed circuit board that utilizes the fact that power transmission in a waveguide is cut-off below a certain frequency. A quasi waveguide cavity is formed in printed circuit board using the top and bottom ground plane of the stripline circuit and using conductive via holes to form the side walls of the cavity. Waveguide cavity mode is launched from the input and output striplines by shorting them to ground. Transformers and matching via hole elements may be used to improve matching. The resulting filter is compact and is highly effective in suppressing low frequency transmissions.